1. Field of the Invention
The present invention relates to a system and method of providing a hydraulic braking system and more specifically to providing a hydraulic braking system in a vehicle that utilizes a hydraulic transmission.
2. Introduction
A hydraulic transmission is a known component which can improve the wear and tear on heavy vehicles. SuperDrive, Inc., in Ohio, is an example of a company that sells a hydraulic transmission as a replacement transmission to the standard mechanical shaft used in most vehicles. FIG. 1 illustrates a basic hydraulic transmission 100. An engine such as a diesel engine 102 is mechanically connected to a hydraulic pump 106.
Hydraulic line 114 and return hydraulic line 116 connect the pump 106 to a hydraulic motor 108 that turns a drive line 112 when hydraulic fluid flows through it. A charge and lube pump 110 is preferably used to pick up hydraulic leakage and for lubrication of surfaces. This charge pump is typically charged to around 350 PSI. A computer control 104 is in communication with the motor 102, pump 106 and motor 108 via lines 118 to control the operation of the hydraulic transmission. This system is a high pressure closed-loop hydraulic cycle and provides for a continuously variable transmission.
The continuously variable transmission (CVT) can handle heavy torque loads and high speeds with improved fuel economy and reduced emissions. A CVT is an automatic transmission that does not shift from one gear to another as the vehicle accelerates, but provides constant, smooth acceleration. The system 100 is coupled to the crankshaft at the rear of the engine in the conventional location for transmissions. The unit installed in the transmission cavity incorporates an axial piston variable hydraulic pump and an axial piston variable hydraulic motor assembled as a single unit. In addition, the system may include a heat exchanger, a reservoir (not shown).
A similar powertrain is shown in U.S. Pat. No. 6,719,080 except that the '080 patent discloses multiple hydraulic lines 23, 24, 25, 26 in FIG. 1. The system 100 only utilizes a single hydraulic loop 114, 116 between the drive pump 106 mechanically connected to the engine 102 and the hydraulic motor 108 connected to the drive line 112.
The system 100 controls the hydraulic pump 106, motor 108 and the diesel engine 102 through the electronic control module 104. The control module 104 manages the engine such that it does not run at a constant RPM. The variability of the engine RPM provides more engine responsiveness and power, and is less wasteful of fuel. For example, the diesel motor 102 may be controlled not to ramp up its RPM as quickly at acceleration and to maintain a more constant RPM while accelerating and decelerating.
This control module 104 manages engine RPM and loading, and pump and motor swash plate position. Fuel economy is further enhanced by the ability of the system to reduce engine RPM while at road speeds. The system 100 increases the ability to provide higher torque at lower engine speeds in effect acting like an overdrive, but providing the ability to continuously maximize the torque output to the rear wheels at all vehicle speeds.
There are many advantages to the hydraulic transmission system 100. However, there are some capabilities for improvement that have not yet been realized. For example, with a hydraulic powertrain, what is needed in the art is a system for improving the efficiency of the transmission and particularly in how to manage braking.